Effect of Organic Manure on Nematodes in Rhizosphere Soil of Soybean Under Continuous Cropping

WANG Duchao, WU Jinggui, LI Jianming

College of Resources and Environmental Sciences, Jilin Agricultural University

Abstract:

【Objective】Studies so far made at home and abroad on soil nematodes are found mostly concentrated on nematodes in bulk soil or non-rhizosphere soil, with relatively less focus on those in rhizosphere soils, let alone on phytophagous nematodes in rhizosphere soils. Therefore, the purpose of this experiment was designed to explore effects of organic manures, prepared mainly out of different agricultural wastes, i.e. pig dung, crop stalks, mushroom residue, forage grass, chicken dropping and fulvic acid bio-manure, on soil nematodes in rhizosphere soil of soybean under a continuous cropping system. Soybean nematodes disease is a disastrous one to soybean production, seriously affecting growth and yield of the crop. 【Method】 By comparing organic manures of different nature in effect on number of nematodes and structure of the nematode community, a method to prevent nematode disease in continuous cropping of soybean was proposed here in the paper. Six different organic materials were selected for comparison and analysis of the two treatments to compare the difference of the rhizosphere soil nematodes. Soil samples were collected from plots applied with different organic manure in the experiment for isolation of nematodes with the shallow disk method and counting of the nematodes under an anatomical lens. Then from each lot, about 100 nematodes were sampled out for identification till genus under an optical microscope. 【Result】 Results show that cp values of the dominant genera and key species in the study were 3, indicating that the nematodes were high in breeding ability and disturbance resistance; after 7 years of continuous cropping of soybean, relative abundance of the omnivorous / predatory nematodes among the trophic groups of soil nematode in the rhizosphere decreased significantly, while that of the plant parasitic nematodes in the rhizosphere increased significantly and that of bacterivores and fungivores increased slightly; the number of nematodes in the rhizosphere of soybean of continuous cropping was significantly higher than in the rhizosphere of soybean of non-continuous cropping; compared with application of chemical fertilizer, application of organic manure retarded growth of plant parasitic nematodes in number. In terms of the effect, the organic manures displayed an order of pig dung > crop stalks > mushroom residue > forage grass > chicken dropping > fulvic acid bio-manure > CK (chemical fertilizer), compared with non-continuous cropping respectively increased by 6.48%, 15.34%, 15.98%, 18.51%, 24.35%, 26.33% and 27.4%. With the continuous cropping going on, the proportion of bacterial nematodes expanded obviously and the expansion was inhibited by application of organic manure and so was the proportion of fungal-feeding nematodes and that of plant parasitic nematodes, though varying in extent. The effect of organic manure was higher than that of chemical fertilizer. In the plots treated with organic manure, plant parasitic nematodes dominated the nematodes community, accounting for more than 50%, while omnivorous nematodes and predatory nematodes were on a decreasing trend. Obviously, application of organic manure has an effect of keeping balance of the soil nematode community.. The ecological index of nematodes was significantly improved by organic manure as compared with CK .【Conclusion】The response of soil nematode to fertilizers depends on quality and nutrient content of the crop and fertilizer or manure; Dominant trophic groups, dominant species and key genera of soil nematodes are effective indicators of health of the agricultural soil and degree of soybean nematodes diseases in the soybean fields.